Millimeters to Inches (mm to in) Online Calculator

Convert length from millimeters (mm) to inches (in) using the exact international relationship between the inch and the SI meter. Suitable for drawings, hardware specs, machining notes, and part catalogs that require dual-dimensioning.

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How to use

1. Enter a value in millimeters.
2. Set the number of decimal places for the result.
3. Select Convert to display inches and the calculation line.
4. Use Copy Result to copy the value.
5. Use Clear All to reset inputs and outputs.
6. The Swap control opens the related calculator for the reverse direction.

Definitions and unit facts

Millimeter (mm) — SI unit of length equal to one thousandth of a meter: 1 mm = 0.001 m. Abbreviation: mm. System: SI. Relation to the inch via the exact definition of the inch gives 1 mm = 0.03937007874 in.

Inch (in) — U.S. customary and Imperial unit of length defined exactly by the metric system since 1959: 1 in = 25.4 mm exactly. Abbreviations: in, ″. System: U.S. customary/Imperial. In SI terms: 1 in = 0.0254 m exactly.

You can visualize the difference between millimeter and inch in this image.

Conversion formula

inches = millimeters ÷ 25.4. Source: NIST — SI Units: Length.

Conversion table

Real-world examples

• Rack unit height (1U): 44.45 mm = 1.7500 in
• 19-inch equipment rack width: 482.60 mm = 19.0000 in
• Compact disc diameter: 120.00 mm = 4.7244 in
• Credit card width (ID-1): 85.60 mm = 3.3701 in
• Credit card height (ID-1): 53.98 mm = 2.1252 in
• U.S. penny diameter: 19.05 mm = 0.7500 in
• U.S. quarter diameter: 24.26 mm = 0.9551 in
• U.S. dime diameter: 17.91 mm = 0.7051 in
• AA battery length (IEC): 50.50 mm = 1.9882 in
• Standard DIN rail width (top hat): 35.00 mm = 1.3780 in

What do you use this calculator for? If you want other online tools, request them in the comments.

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